The cable distribution system for television communication has become a substantial part of television broadcast operation. In a typical cable system, a so-called headend facility is maintained by the cable system operator which provides a plurality of television programs modulated upon a corresponding plurality of television channel frequencies. A plurality of decoders are operative within the subscriber homes and other facilities which are coupled to the headend of the cable system by a distribution network. The function of the receiver decoders is to provide channel selection and recovery of the program material for use by the subscriber's television receiver. In most systems, the headend includes the capability for scrambling some or all of the program channels to render them unviewable without a corresponding descrambling process within the receiver decoders. This descrambling capability is controlled in a process known as authorization.
The cable headend system also provides operational information together with the programming material such as program or channel authorization, channel mapping and other features which require communication between the headend and the system decoders. In some cable systems, this communication takes place in a protocol known as in-band communication by inserting the additional information into portions of the program signal. These systems are referred to as in-band because of the communication taking place within the channel bandwidth of the television program channel.
In other systems, the in-band communication is supplemented by an out of band communication capability so named because of the use of communication channels outside the television program channel. Typically, an available broadcast frequency such as a FM radio frequency is used to provide this out of band communication. In such systems, data from the head end controller is modulated upon an FM radio frequency carrier and received by FM receivers within the system decoders. The modulated data is recovered by the decoder receivers and used to operate the decoders in response to the headend data.
The desire to effectively use the out of band communication capability to maximize system flexibility and potential while avoiding undue operational complexity and system difficulties creates a continuing need in the art for evermore improved cable communication systems.
Accordingly, it is a general object of the present invention to provide an improved cable communication system. It is a more particular object of the present invention to provide an improved out of band cable communication system.